This invention relates to method and means for making helical races. It relates more particularly to a technique for inscribing helical races having a uniform cross-section in a curved work-piece.
There has recently been developed a transmission which transmits power from an input shaft to an output shaft by way of a multiplicity of circular ball bearing units driven by a worm on the output shaft and whose bearings follow spaced-apart, helical races inscribed in a wall of a toroidal enclosure. A transmission such as this is disclosed in U.S. Pat. No. Re. 26,476.
It has been found that considerable care must be taken in fabricating the toroidal enclosures for such transmissions so that the races inscribed in the enclosures have uniform cross-section and relative pitch along their entire lengths. Indeed, it has not been possible heretofore to manufacture toroidal helical enclosures which meet the mathematical requirements of constant cross section of the races and varying lead angle in accordance with the requirement of uniform rotational output motion.
It should be clearly understood at this point that it is imperative that the toroidal helical races in such transmissions be extremely uniform and precisely related to the axis of the helix which coincides with the axis of rotation of the worm in order for the transmission to function properly. Without these constraints, the bearings are loaded unevenly contributing to excessive bearing wear. Further, certain bearings in the bearing units begin to disengage from the driving worm at certain times. These "loose" bearings begin to trail the others because they are not rotated enough so that they tend to "buck" the advancement of the bearing units within the housing.
Accordingly, the present invention aims to provide a method for making accurately formed helical races in a curved work-piece.
Another object of the invention is to provide a method for making races of this type having a uniform cross-section.
Yet another object of the invention is to provide a method for inscribing helical races having a uniform cross-section in the surface of a toroidal enclosure.
A further object of the invention is to provide apparatus for inscribing accurately toroidal helical races in a toroidal enclosure which are precisely positioned relative to each other and also to the axis of the enclosure.
Other objects will, in part, be obvious and will, in part, appear hereinafter.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying the features of construction, combination of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed description, and the scope of the invention will be indicated in the claims.
In general, the present apparatus forms helical races in a curved work-piece by performing a double rotation of the cutting tool and work-piece about orthogonal axes. The rotations are synchronized so that the tool is maintained at a uniform attack angle relative to the work-piece as the races are formed with the result that the races have a uniform cross-section along their entire lengths.
The apparatus supports the work-piece on a rotary work-table which turns about a vertical axis. The cutting tool is supported directly above the work-table by a rotary yoke which turns about a horizontal axis. The work-table and yoke operate together so that when the work-table is turned by a suitable electrical motor, the cutting tool is swung through an arc whose radius corresponds to the radius of the helical races being formed in the work-piece. The pitch of the races on the other hand is determined by the ratio between the advance of the work-table and the advance of the yoke.
The present apparatus greatly simplifies the formation of mathematically correct, even helical races in toroidal transmissions of the type described in the above patent. As a result of the precisely controlled double rotation of the cutting tool and work-piece, helical races can be formed in toroidal transmission enclosures which are uniform cross-section and are precisely positioned relative to each other and are precisely positioned relative to the axis of the toroidal enclosure. Resultantly, the bearings in transmissions made by this technique all share the applied load equally and are uniformly engaged by the driving worm. Consequently, bearing wear is minimized and the transmission operates at maximum efficiency. Still, however, the present apparatus is relatively easy to operate and maintain.